When Speed Goes Up, Does Safety Go Down?

During a typical day on the Southern California freeway system, dozens of cars crash into each other, leaving a trail of blood, broken glass and big insurance claims in their wake. It’s the price of mobility in a region that worships automobiles, but some experts are asking whether the recent enactment of higher speed limits on urban freeways is worth the inevitably higher cost of more accidents.

The Insurance Institute for Highway Safety, a group funded by the industry, has recently completed a limited study of how higher speed limits have affected driving habits in Southern California and Texas. When authorities raised the speed limits on urban freeways from 55 mph to 65 mph in some parts of Southern California and in Houston, the impact was a sharp jump in the percentage of motorists who drive faster than 70 mph, the institute found.

Engineers for the institute say that the ramps, curves and other features of many urban freeways were not designed to the 70 mph standards of interstate freeways. “It is quite clear that there is going to be a consequence of more injuries and deaths,” said Allan Williams, vice president for research at the institute.

The study involved clocking speeds using a photo radar system at the roadside. Four locations in the Riverside area were examined: Route 91, I-215 and two spots along Route 60. Engineers took measurements of 1,000 cars a week before the speed limits were raised. Then, at the same hour of the day, another 1,000 cars were clocked after new speed limits were posted. The study recorded about a one-third increase in the number of cars exceeding 70 mph, which is now up to 37%.

Both the California Department of Transportation and the California Highway Patrol, which jointly determined where speed limits would be raised, say higher speeds will not necessarily jeopardize safety.

Although they vow to reduce speed limits if they find unsafe conditions, the fact that the extent of speeding above 70 mph has increased is not reason enough to act, said Steve Kohler, a CHP spokesman. The agencies raised speeds from 55 to 65 on 4,200 miles of freeways in the state and from 65 to 70 on another 1,200 miles in December and January.

Within Southern California, the only major exceptions to 65 mph limits are on portions of the 405, 101, 110 and 5 freeways. Accident data between Dec. 17 and March 31 indicates a 2.6% increase in collisions statewide and only a .9% increase in collisions attributable to excessive speed, Kohler said.

But Richard Retting, a traffic engineer at the safety institute, dismissed that data as inconclusive, and noted that cars going faster but still within the new higher speed limits are, by definition, not going at excessive speed.

* Vartabedian cannot answer mail personally but will attempt to respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, 1875 I St. N.W., No. 1100, Washington, DC 20006.